Radio wave absorber, electromagnetic field measurement system and radiated immunity system

ABSTRACT

A radio wave absorber for use in an electromagnetic field probe that measures an electromagnetic field by means of an antenna section provided therewith, the radio wave absorber including: a first end section; a second end section that is located at a position opposite the first end section; and an intermediate section that is located between the first and second end sections, the intermediate section having outer dimension and thickness that increase in accordance with a distance from the first end section toward the second end section.

This application is a divisional of U.S. patent application Ser. No.12/714,947, filed Mar. 1, 2010, which is a divisional of U.S. patentapplication Ser. No. 11/222,223, filed Sep. 9, 2005, which claimspriority to Japanese Patent Application Nos. 2005-137701, 2005-137703,and 2005-137705, filed May 10, 2005, all of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electromagnetic field measurementsystem for measuring an electromagnetic field by means of anelectromagnetic field probe, and to a radiated immunity system.

The present invention also relates to an electromagnetic field probeused for measuring an electromagnetic field, and to a radio waveabsorber and an exterior body that cover an electromagnetic field probefor measuring an electromagnetic field.

2. Description of the Related Art

Many electromagnetic wave sources, such as electronic equipment,electrical appliances, and radio equipment, have recently becomeprevalent in home. Electromagnetic waves originating from theelectromagnetic wave sources have the potential risk of affecting theambient electromagnetic-wave environment in various manners, and theelectronic equipment, or the like, which becomes the source ofelectromagnetic waves may also be affected by the electromagneticenvironment originating from another electromagnetic wave source. Forthese reasons, the electronic equipment is desired to prevent emissionof electromagnetic waves outside the equipment and to have EMC(Electro-Magnetic Compatibility) measures of resistance to the ambientelectromagnetic environment.

The EMC measures must be adopted so as to address emission or EMI(Electro-Magnetic Interface) and immunity or EMS (Electro-MagneticSusceptibility).

IEC61000-4-3 is available as upstandards for evaluating immunity of suchelectronic equipment or the like. In order to evaluate resistance ofelectronic equipment to electromagnetic interference, a test defined bythe regulations is conducted by exposing a device under test or EUT(Equipment under Test) to electromagnetic interference to whichelectronic equipment is presumed to be exposed, and observing thebehavior of the device or EUT.

A specific configuration for an immunity test is described inJP-A-4-029069. The document JP-A-4-029069 describes the steps of:emitting electromagnetic wave noise toward a device under test placed ina radio wave shielded chamber whose wall surfaces are filled with radioabsorbers; and a technician monitoring whether or not the device undertest performs faulty operation when exposed to this disturbance factor,by way of a monitor. Evaluation of immunity of such electronic equipmentto radiation noise entails prevention of influence of electromagneticwave noise to the outside and highly accurate measurement of acharacteristic.

In order to conduct an immunity test, formation of a uniform electricfield region within the radio wave shielded chamber must have beenascertained in advance. Ascertaining the performance of such a radiowave shielded chamber requires measuring the value of electric fieldintensity in the radio wave shielded chamber through use of a fieldsensor; and recording the resultant deviation.

As to a field sensor, a product capable of measuring a broadbandfrequency exceeding 1 GHz is commercially available (e.g., a probemanufactured by ETSLINDGREN Co., Ltd.), and the value of field intensityin the radio wave shielded chamber is measured by use of the fieldsensor.

SUMMARY OF THE INVENTION

However, among other problems, when the frequency has exceeded 1 GHz,the commercially-available field sensor encounters a problem ofincreased frequency of occurrence of a measurement error. This problemis considered to be attributable to reflection of an electromagneticwave due to the structure of the field sensor. In order to minimize sucha phenomenon of reflection of an electromagnetic wave, there has alreadybeen proposed a method for effecting measurement by tilting the fieldsensor to a 45-degree angle or a 33.5-degree angle. However, this methodhas failed to prevent occurrence of the phenomenon of reflection of anelectromagnetic wave over a wide broadband frequency spectrum.

The present invention has been made in view of the above circumstancesand provides a radio wave absorber, an electromagnetic field measurementsystem, and a radiated immunity system.

According to a first aspect of the invention, there is provided a radiowave absorber used for in an electromagnetic field probe that measuresan electromagnetic field by means of an antenna section providedtherewith, the radio wave absorber including: a first end section; asecond end section that is located at a position opposite the first endsection; and an intermediate section that is located between the firstand second end sections, the intermediate section having outer dimensionand thickness that increase in accordance with a distance from the firstend section toward the second end section.

According to a second aspect of the invention, there is provided anexterior body used in an electromagnetic field probe having a radio wavereflector extending from an antenna section to a box section, theexterior body including: a radio wave absorber; a housing section thatis provided in the radio wave absorber and houses the radio wavereflector and the box section of the electromagnetic field probe; anantenna side edge section located at a portion of the radio waveabsorber facing the antenna section of the electromagnetic field probe;and a box side edge section located at a portion of the radio waveabsorber facing the box section of the electromagnetic field probe,wherein the exterior body has outer dimension and thickness thatincreases with an increase in distance from the antenna side edgesection toward the box side edge section.

According to a third aspect of the invention, there is provided anexterior body used in an electromagnetic field probe having a radio wavereflector extending from an antenna section to a box section, theexterior body including: a first exterior section that forms a part ofthe exterior body; and a second exterior section that forms a part ofthe exterior body and engages with the first exterior section in asplitable manner; wherein each of the first and second exterior sectionshas: a radio wave absorber that covers the radio wave reflector of theelectromagnetic field probe; and a radio wave transmission body that isprovided on an exterior surface of the radio wave absorber, wherein theradio wave absorber includes an antenna side edge section located at aportion of the radio wave absorber facing the antenna section of theelectromagnetic field probe; and a box side edge section located at aportion of the radio wave absorber facing the box section of theelectromagnetic field probe, wherein the exterior body has outerdimension and thickness that increases with an increase in distance fromthe antenna side edge section toward the box side edge section.

According to a fourth aspect of the invention, there is provided anelectromagnetic field probe including: an antenna section; a radio wavereflector extending from the antenna section; and a radio wave absorberthat surrounds a circumference of the radio wave reflector and isprovided with a portion having outer dimension and thickness thatincrease in accordance with a distance from the antenna section.

According to a fifth aspect of the invention, there is provided anelectromagnetic field probe including: an antenna section that measuresan electromagnetic field; a wire connected to the antenna section; ashielding member that shields the wire; a box section that receives aninput of a measurement result of the antenna section by way of the wire;and a radio wave absorber that surrounds circumferences of the shieldingmember and the box section, wherein the radio wave absorber is providedwith a portion having outer dimension and thickness that increase inaccordance with a distance from the antenna section.

According to a sixth aspect of the invention, there is provided anelectromagnetic field measurement system including: an electromagneticfield probe having an antenna section that measures an electromagneticfield, and a radio wave reflector extending from the antenna section; aradio wave absorber that is mounted to the radio wave reflector of theelectromagnetic field probe and has a portion having outer dimension andthickness increase in accordance with an increase in a distance from theantenna section of the electromagnetic field probe; and a proberetaining member that retains the electromagnetic field probe.

According to a seventh aspect of the invention, there is provided aradiated immunity system for measuring uniformity of an electromagneticfield required for a radiated immunity test, the radiated immunitysystem including: a radiation antenna; an antenna section that measuresan electromagnetic field by means of the radiation antenna; a wireconnected to the antenna section a shielding member that shields thewire; and a radio wave absorber that surrounds a circumference of theshielding member, the radio wave absorber having outer dimension andthickness that increase in accordance with a distance from the antennasection.

According to an eighth aspect of the invention, there is provided aradio wave absorber for use in an electromagnetic field probe thatmeasures an electromagnetic field by means of an antenna sectionprovided therewith, the radio wave absorber including: a proximal endsection that is provided close to the antenna section; and a distal endsection that is located at a position opposite the proximal end sectionand remote from the antenna section, wherein a cross-sectional area ofthe radio wave absorber increases in accordance with a distance from theproximal end section toward the distal end section, and wherein thecross-sectional area is configured to be maximum at an intermediatesection between the proximal end section and the distal end section orat the position of the distal end section.

According to a ninth aspect of the invention, there is provided anexterior body used in an electromagnetic field probe having a radio wavereflector extending from an antenna section to a box section, theexterior body including: a radio wave absorber; a housing section thatis provided in the radio wave absorber and houses the radio wavereflector and the box section of the electromagnetic field probe; anantenna side edge section located at a portion of the radio waveabsorber facing the antenna section of the electromagnetic field probe;and a box side edge section located at a portion of the radio waveabsorber facing the box section of the electromagnetic field probe,wherein a cross-sectional area of the radio wave absorber increases inaccordance with a distance from the antenna side edge section toward thebox side edge section, and wherein the cross-sectional area isconfigured to be maximum at an intermediate section between the antennaside edge section and the box side edge section or at the position ofthe box side edge section.

According to a tenth aspect of the invention, there is provided anexterior body used in an electromagnetic field probe having a radio wavereflector extending from an antenna section to a box section, theexterior body including: a first exterior section that forms a part ofthe exterior body; and a second exterior section that forms a part ofthe exterior body and engages with the first exterior section in asplitable manner; wherein each of the first and second exterior sectionshas: a radio wave absorber that covers the radio wave reflector of theelectromagnetic field probe; and a radio wave transmission body that isprovided on an exterior surface of the radio wave absorber, wherein theradio wave absorber has a proximal end section provided close to theantenna section of the electromagnetic field probe and a distal endsection provided remote from the antenna section, wherein the radio waveabsorber has a cross-sectional area that increases in accordance with adistance from the proximal end section toward the distal end section,and wherein the cross-sectional area is configured to be maximum at anintermediate section between the proximal end section and the distal endsection or at the position of the distal end section.

According to an eleventh aspect of the invention, there is provided anelectromagnetic field probe including: an antenna section; a wireconnected to the antenna section; a support member that supports theantenna section; and a longitudinal radio wave absorber surrounding acircumference of the support member, wherein the radio wave absorber hasa proximal end section provided close to the antenna section and adistal end section provided remote from the antenna section, wherein across-sectional area of the radio wave absorber increases in accordancewith a distance from the proximal end section toward the distal endsection, and wherein the cross-sectional area is configured to bemaximum at an intermediate position between the proximal end section andthe distal end section or at the position of the distal end section.

According to a twelfth aspect of the invention, there is provided anelectromagnetic field probe including: an antenna section that measuresan electromagnetic field; a wire connected to the antenna section; ashielding member that shields the wire; a box section that receives aninput of a measurement result of the antenna section by way of the wire;and a radio wave absorber that surrounds circumferences of the shieldingmember and the box section, wherein the radio wave absorber has aproximal end section provided close to the antenna section and a distalend section provided remote from the antenna section, wherein across-sectional area of the radio wave absorber increases in accordancewith a distance from the proximal end section toward the distal endsection, and wherein the cross-sectional area is configured to bemaximum at an intermediate position between the proximal end section andthe distal end section or at the position of the distal end section.

According to a thirteenth aspect of the invention, there is provided anelectromagnetic field measurement system including: an electromagneticfield probe having an antenna section that measures an electromagneticfield, a retaining member that retains the antenna section, and a boxsection that receives an input of result of measurement performed by theantenna section; a radio wave absorber that surrounds a circumference ofthe retaining member of the electromagnetic field probe and acircumference of the box section; and a cable that extends from the boxsection of the electromagnetic field probe, wherein the radio waveabsorber has a proximal end section provided close to the antennasection of the electromagnetic field probe and a distal end sectionprovided remote from the antenna section, wherein a cross-sectional areaof the radio wave absorber increases in accordance with a distance fromthe proximal end section toward the distal end section; and wherein thecross-sectional area is configured to be maximum at an intermediateposition between the proximal end section and the distal end section orat the position of the distal end section.

According to a fourteenth aspect of the invention, there is provided aradiated immunity system for measuring uniformity of an electromagneticfield required for a radiated immunity test, the radiated immunitysystem including: a radiation antenna; an antenna section that measuresan electromagnetic field by means of the radiation antenna; a wireconnected to the antenna section; a shielding member that shields thewire; and a radio wave absorber that surrounds a circumference of theshielding member, wherein the radio wave absorber has a proximal endsection provided close to the antenna section of the electromagneticfield probe and a distal end section provided remote from the antennasection, wherein a cross-sectional area of the radio wave absorberincreases in accordance with a distance from the proximal end sectiontoward the distal end section; and wherein the cross-sectional area isconfigured to be maximum at an intermediate position between theproximal end section and the distal end section or at the position ofthe distal end section.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a schematic block diagram showing a radiation field immunitysystem according to an embodiment of the present invention;

FIG. 2 is a block diagram showing the configuration of the radiationfield immunity system;

FIG. 3 is a descriptive view for describing calibration points in auniform electromagnetic field range;

FIG. 4 is a schematic block diagram of a probe main body;

FIGS. 5A and 5B are block diagrams showing that a radio wave absorber isattached to the probe main body;

FIGS. 6A and 6B are block diagrams showing that a radio wave absorber isattached to the probe main body;

FIGS. 7A and 7B are block diagrams showing that a radio wave absorber isattached to the probe main body;

FIGS. 8A and 8B are block diagrams showing that a radio wave absorber isattached to the probe main body;

FIGS. 9A and 9B are block diagrams showing that a radio wave absorber isattached to the probe main body;

FIGS. 10A and 10B are block diagrams showing that a radio wave absorberis attached to the probe main body;

FIGS. 11A and 11B are block diagrams showing that a radio wave absorberis attached to the probe main body;

FIGS. 12A and 12B are block diagrams showing that a radio wave absorberis attached to the probe main body;

FIGS. 13A and 13B are block diagrams showing that a radio wave absorberand polystyrene foam are attached to the probe main body;

FIGS. 14A and 14B are block diagrams showing that a radio wave absorberand polystyrene foam are attached to the probe main body;

FIGS. 15A and 15B are graphs showing results of examples;

FIG. 16 is a graph showing variations computed from the test results;

FIG. 17 is a block diagram showing a probe of a third example;

FIG. 18 is a block diagram showing a probe of a third comparativeexample;

FIGS. 19A and 19B are graphs showing results of examples;

FIG. 20 is a graph showing variations computed from the test results;and

FIG. 21 is a block diagram showing a probe of a second comparativeexample.

DETAILED DESCRIPTION OF THE EMBODIMENT

An embodiment of the invention will be described with reference to thedrawings.

FIG. 1 is a schematic block diagram showing a radiation field immunitysystem according to an embodiment. An electromagnetic field immunitysystem shown in FIG. 1 shows a structure for calibrating the electricfield uniformity of radiation field immunity test.

As shown in FIG. 1, the radiation field immunity system has a radio waveshielded chamber 10. The radio wave shielded chamber 10 is for creatinga desired electromagnetic environment isolated from the outside. Namely,the radio wave shielded chamber 10 prevents entrance of a radio wavefrom the outside, as well as preventing leakage of radio wave noiseemitted from an antenna 20 to the outside, which will be described laterand is set in the radio wave shielded chamber 10. Unillustrated radiowave absorbers for absorbing electromagnetic waves are provided on thewalls and ceiling of the radio wave shielded chamber 10. An additionalradio wave absorber 11 is placed in a predetermined area of the floorfor setting, in the radio wave shielded chamber 10, an electromagneticwave damping characteristic required for a quasi-anechoic chamber.Specifically, the additional radio wave absorber 11 is placed at aposition on the floor between the antenna 20 and a probe 30. A uniformelectromagnetic field area (Uniform Area), which will be describedlater, is set in the radio wave shielded chamber 10.

The antenna (electromagnetic field generation means) 20 and the probe (afield sensor or electric field sensor) 30 are provided in the radio waveshielded chamber 10. This antenna 20 is for generating anelectromagnetic field in the radio wave shielded chamber 10 and isattached to an upstand 21. The probe 30 includes a probe main body 40(see FIG. 4) and radio wave absorbers attached to the probe main body40. The probe main body 40 is an isotropic electromagnetic field probeand corresponds to a dedicated measurement instrument designed formeasuring an electromagnetic environment. The probe 30 is for measuringan intensity value (electric field intensity) of the electromagneticfield developed in the antenna 20, and is attached to an upstand 31 soas to assume a predetermined positional relationship with respect to theantenna 20.

FIG. 2 is a block diagram showing the configuration of a radiation fieldimmunity system.

As shown in FIG. 2, the radiated immunity system includes a signalgenerator 51; an amplifier 52; a directional coupler 53; a power meter(measurement instrument) 54; and a PC (personal computer) 55. The signalgenerator 51 is a device for generating a modulated voltage waveformdetermined by specifications. The amplifier 52 is a device whichamplifies an output from the signal generator 51 to thus acquire powerrequired to emit a sufficient electromagnetic field. The directionalcoupler 53 is a device which is connected to the antenna 20 by means ofa cable 22 and is used for routing an RF (Radio Frequency) signal and amicrowave signal, both of which are to be used for isolating,separating, or connecting a signal. The power meter 54 is a device formeasuring the intensity (power) of a high-frequency signal with highaccuracy. The PC 55 is connected to the signal generator 51, the powermeter 54, and the probe 30. Specifically, the signal generator 51 andthe amplifier 52 are controlled by the PC 55 by way of an unillustratedbus. Moreover, the PC 55 is connected to the probe 30 by means ofexchanging signals by way of an optical fiber 55 a (see FIG. 1).

As mentioned above, as compared with electrical transmission, use of thetransmission system formed from the optical fiber 55 a enablesnoise-resistant, faster, and longer-distance transmission.

FIG. 3 is a descriptive view for describing calibration points withinthe uniform electromagnetic field range shown in FIG. 1.

As shown in FIG. 1, the uniform electromagnetic field range shown inFIG. 3 is a vertical plane which is spaced 3 meters away from theantenna 20 and measures 1.5 meters by 1.5 meters. A total of 16calibration points are set at uniform intervals of 0.5 meters within theuniform electromagnetic field area. Such a uniform electromagnetic fieldarea is set at a height of 0.8 meters from the floor. Electric fieldintensity values of the respective calibration points are measuredthrough use of the probe 30. After the mean value has been computed bythe PC 55 on the basis of the data pertaining to the measured sixteencalibration points, a deviation is computed by subtracting the meanvalue from the respective sets of data. Thus, the performance of theradio wave shielded chamber 10 is ascertained.

FIG. 4 is a schematic block diagram of the probe main body 40.

As shown in FIG. 4, the probe main body 40 includes ahead section(antenna section) 41, a pipe section (a radio wave reflector, aretaining member, and shielding member) 42, and a box section 43. Thepipe section 42 extends from the box section 43, and the head section 41is attached to the extremity of the pipe section 42. Put another way,the head section 41 is provided at one end of the pipe section 42, andthe box section 43 is disposed at the other end of the pipe section 42.

The head section 41 is spherical, and a small receiving antenna (anisotropic antenna) 41 a is provided in the head section 41. The pipesection 42 is formed from a steel pipe member for shielding purpose, anda cable (line material) 42 a is inserted in the steel pipe member so asto extend in the axial direction thereof. The box section 43 is made ofmetal and is formed in a shape of a box. The box section 43 houses anunillustrated circuit board, which is used for performing arithmeticoperation through use of the result received by the head section 41 andeffects E/O conversion, and an unillustrated rechargeable battery. Anoptical signal output from the unillustrated circuit board, or the like,is transmitted to the PC 55 (see FIG. 2) disposed outside the radio waveshielded chamber 10 by way of the optical cable 55 a.

In the probe main body 40 shown in FIG. 4, the cable 42 a connected tothe antenna 41 a is shielded by the pipe section 42. However, in a casewhere the cable 42 a itself has a shielding function, variousmodifications are conceivable.

For instance, in a conceivable configuration, an unillustratednon-metallic member, such as resin, is provided for retaining the headsection 41 in lieu of the pipe section 42 made from a steel pipe. Inthat case, the cable 42 a can be routed over an exterior surface of theunillustrated non-metallic member.

In another configuration, for example, the head section 41 is retainedby polystyrene foam to be described later (see FIGS. 13A-14B). In thatcase, there can be realized a simple configuration, wherein solely thecable 42 a is arranged in a radio wave absorber (see reference numeral110 in FIGS. 5A and 5B) to be described later.

Shapes, or the like, of various types of radio wave absorbers attachedto the probe main body 40 will now be described by reference to FIGS. 5Ato 12B. FIGS. 5 to 12 are block diagrams showing a status in which aradio wave absorber is attached to the probe main body 40. FIGS. 5A, 6A,7A, 8A, 9A, 10A, 11A, and 12A are front views showing a two-piece radiowave absorber with one of the pieces being removed, and FIGS. 5B, 6B,7B, 8B, 9B, 10B, 11B, and 12B are left-side views showing the two-pieceradio wave absorber with both pieces attached together.

The radio wave absorber to be described below has an elongated internalspace which corresponds to the shape of the attached probe main body 40.The radio wave absorber to be described below is formed to have auniform concentration of carbon.

A radio wave absorber 110 shown in FIGS. 5A and 5B is formed in a shapeof a truncated cone, wherein a cone is cut by a plane substantiallyparallel to a lower bottom surface (a distal end, and a box side edgesection) 111 to thus form an upper bottom surface (a proximal end, andan antenna side edge section) 112. Specifically, a tapered shape(pyramid shape) having a given tilt angle is formed over the entirety ofthe radio wave absorber 110. The outer shape of the radio wave absorber110 is such that the outer shape and thickness of the radio waveabsorber become larger as a distance from the head section 41 of theprobe main body 40 increases in the axial direction of the pipe section42. From another viewpoint, the radio wave absorber 110 assumes theouter shape such that the cross-sectional area of the upper bottomsurface 112 is smaller than that of the lower bottom surface 111. Fromyet another viewpoint, the outer shape of the radio wave absorber 110 issuch that the cross-sectional area becomes larger as a distance from theupper bottom surface 112 increases toward the lower bottom surface 111and such that the cross-sectional area becomes maximum at the positionof the lower bottom surface 111.

When the radio wave absorber 110 having such a tapered shape is viewedfrom the head section 41 of the probe main body 40, the thickness of theradio wave absorber 110 (along the axis of the pipe section 42) changeswhen the position changes along the radial direction of the radio waveabsorber 110. Therefore, even in the case of the radio wave absorber 110having a uniform concentration of carbon, the concentration of carbonchanges in the radial direction of the radio wave absorber 110. As thedistance to the pipe section 42 of the probe main body 40 becomessmaller, the carbon concentration increases. Conversely, when thedistance to the pipe section 42 becomes greater, the carbonconcentration decreases. Therefore, a broadband radio wave from theantenna 20 (see FIG. 1) can be absorbed, and occurrence of resonance ina broadband frequency spectrum can be suppressed. As a result ofsuppression of occurrence of resonance in such a broadband frequencyspectrum, transformation of data, which would otherwise arise in spiteof the probe 30 being placed in the same position or which wouldotherwise arise according to a probe 30 employed, can be prevented, tothus enhance reproducibility of the probe.

The radio wave absorber 110 covers the pipe section and the box section43 of the probe main body 40. Therefore, resonance of the pipe section42 can be suppressed by the radio wave absorber 110, and reflection of aradio wave, which would otherwise be caused by the box section 43, canbe suppressed by the radio wave absorber 110.

The upper bottom surface 112 is situated at a position close to the headsection 41 of the probe main body 40, and the lower bottom surface 111is situated at a position close to the box section 43 of the probe mainbody 40. The upper bottom surface 112 is smaller in cross-sectional areathan the lower bottom area 111. In addition, the upper bottom surface112 is smaller than the outer diameter of the head section 41 of theprobe main body 40. Therefore, the radio wave reflected from the radiowave absorber 110 can be prevented from causing interference with thehead section 41.

The radio wave absorber 110 has a structure such that the absorber issplit into two pieces along a mating face or a split face 110 a. Theradio wave absorber 110 is formed from two members (a first radio waveabsorber portion and a second radio wave absorber portion). As a resultof the radio wave absorber 110 having a split structure, ease ofmaintenance of the unillustrated rechargeable battery, or the like,housed in the box section 43 of the probe main body 40 can be enhancedas mentioned previously. The number of pieces into which the radio waveabsorber 110 are to be separated may be any number other than two.

A radio wave absorber 120 shown in FIGS. 6A and 6B is formed in a shapemade by combining together a truncated cone and a cylinder located onthe lower bottom surface of the truncated cone. Specifically, the boxsection 43 of the probe main body 40 in the radio wave absorber 120 doesnot assume any tapered shape. The radio wave absorber 120 covers thepipe section 42 and the box section 43 of the probe main body 40. Theradio wave absorber 120 has a structure such that the absorber is splitinto two pieces by a split face 120 a.

A radio wave absorber 130 shown in FIGS. 7A and 7B is formed in a shapemade by combining together two truncated cones having different heights;in other words, a shape made by joining lower bottom surfaces of twotruncated cones. Specifically, the radio wave absorber 130 assumes areversely-tapered shape, wherein the inclination is inverted at someintermediate point on the tapered surface. The radio wave absorber 130covers a pipe section 42 and a box section 43 of a probe main body 40.The radio wave absorber 130 has a structure such that the absorber issplit into two pieces along a split face 130 a.

A radio wave absorber 140 shown in FIGS. 8A and 8B is formed in a shapeformed by combining together a truncated cone, a cylinder located on thelower surface of the truncated cone, and a cylinder (flange section)situated on the upper bottom surface of the truncated cone.Specifically, the head section 41 and the box section 43 of the probemain body 40 in the radio wave absorber 140 do not assume any taperedshapes. Moreover, the radio wave absorber 140 covers the pipe section 42and the box section 43 of the probe main body 40. The radio waveabsorber 140 has a structure such that the absorber is split into twopieces along a split face 140 a.

A radio wave absorber 150 shown in FIGS. 9A and 9B is formed in a shapeof a so-called rugby ball or an substantially-bellshaped form, which isone-half of a substantially oval shape cut at some point on the majoraxis. Put another way, the radio wave absorber 150 is formed with anouter shape made by bulging a side surface of an substantially truncatedcone; namely, the inclination angle of the tapered shape of the radiowave absorber 150 is not constant. The radio wave absorber 150 coversthe pipe section 42 and the box section 43 of the probe main body 40.The radio wave absorber 150 has a structure such that the absorber issplit into two pieces along a split face 150 a.

A radio wave absorber 160 shown in FIGS. 10A and 10B is formed in ashape made by combining together a truncated pyramid, and a square polelocated on the lower bottom surface of the truncated pyramid.Specifically, the box section 43 of the probe main body 40 in the radiowave absorber 160 does not assume any tapered shape. The radio waveabsorber 160 covers the pipe section 42 and the box section 43 of theprobe main body 40. The radio wave absorber 160 assumes a structure suchthat the absorber is split into two pieces along a split face 160 a.Although the shape of a truncated pyramid is illustrated in FIGS. 10Aand 10B, adoption of a prismoid, such as a delta cone or a pentagonalcone, is also conceivable.

A radio wave absorber 170 shown in FIGS. 11A and 11B is formed in ashape of a truncated pyramid, and covers the pipe section 42 and a frontsurface 43 a of the box section 43, both of which belong to the probemain body 40. The front surface 43 a corresponds to a surface of the boxsection 43 facing the head section 41. As mentioned above, according tothe embodiment shown in FIGS. 11A and 11B, the radio wave absorber 170covers only the front surface 43 a of the box section 43. Moreover, theradio wave absorber 170 has a structure such that the absorber is splitinto two pieces along a split face 170 a.

A radio wave absorber 180 shown in FIGS. 12A and 12B is formed in ashape of a truncated cone. Here, the probe main body 40 shown in FIGS.12A and 12B is of a type which does not have the box section 43.Specifically, the probe main body 40 has the head section 41 and thepipe section 42, but does not have the box section 43. Therefore, theradio wave absorber 180 only covers the pipe section 42. One end of theradio wave absorber 180 is in contact with the head section 41.

By reference to FIGS. 13A tO 14B, there will now be described a casewhere a radio wave absorber and polystyrene foam are attached to theprobe main body 40. FIGS. 13A to 14B are block diagrams showing a statewhere a radio wave absorber and polystyrene foam are attached to theprobe main body 40. FIG. 13A is a longitudinal cross-sectional view, andFIG. 13B is a left elevation view. FIG. 14A is a front view showing thatone of a two-split exterior body 200 (a radio wave absorber 201 andpolystyrene foam 202) is removed, and FIG. 14B is a left elevation viewshowing that the two pieces of the two-split exterior body 200 areattached together.

In the case shown in FIGS. 13A and 13B, the radio wave absorber 160shown in FIGS. 10A and 10B is covered with polystyrene foam (a posturedefining member, a retaining section, a radio wave transmission body,and a maintaining member) 190. As shown in FIG. 13B, the polystyrenefoam 190 has a structure such that the polystyrene foam is split intotwo pieces along a split face 190 a. More specifically, the polystyrenefoam 190 is formed from a first section (a first retaining section) anda second section (a second retaining section). This split face 190 aextends in a direction substantially orthogonal to the split face 160 aof the radio wave absorber 160. As mentioned above, in the case shown inFIGS. 13A and 13B, there is adopted a configuration such that thetwo-split radio wave absorber 160 is sandwiched between the pieces ofthe polystyrene foam 190.

As shown in FIG. 13B, the polystyrene foam 190 is provided with latchsections 190 b. More specifically, a boss-shaped section is formed inone of the two pieces of the two-split polystyrene foam 190, and amating section which mates with the boss-shaped section is formed on theother piece. Therefore, two pieces of the two-split polystyrene foam 190can be coupled together with reliability.

In the case shown in FIGS. 13A and 13B, after the probe main body 40 hasbeen covered with the radio wave absorber 160, the radio wave absorber160 can be sandwiched between the pieces of the polystyrene foam 190,whereby the probe main body 40 can be assembled. By means of such anassembly, the polystyrene foam 190 comes into contact with an exteriorsurface of the radio wave absorber 160, so that the posture of the radiowave absorber 160 can be held in a horizontal position.

The majority of mass of the polystyrene foam 190 is occupied by air. Forthis reason, even when the radio wave absorber 160 is enfolded with thepolystyrene foam 190, no problems arise in the state of a radio wave. Itis preferable to use polystyrene foam of a high expansion ratio as thepolystyrene foam 190.

In the case shown in FIGS. 14A and 14B, the radio wave absorber 201 andthe polystyrene foam 202 are formed into one piece, to thus constitutethe exterior body 200. Therefore, the number of parts handled by anoperator can be diminished, and operability can be enhanced.

In this exterior body 200, the polystyrene foam 202 runs along theentire perimeter of the radio wave absorber 201. More specifically, thepolystyrene foam (structure body) 202 is interposed between the probemain body 40 and the radio wave absorber 201. By means of such aconfiguration, even when the radio wave absorber 201 is formed from aneasily-deformable material, the load attributable to the weight of theprobe main body 40 can be imposed on the polystyrene foam 202, so thatdeformation of the radio wave absorber 201 can be prevented. Therefore,an intended advantage attributable to the shape of the radio waveabsorber 201; that is, an advantage of a broadband radio wave absorber,or the like, can be yielded sufficiently.

The exterior body 200 has a structure such that the exterior body issplit into two pieces along a split face 200 a. Specifically, theexterior body 200 is formed from a first exterior section and a secondexterior section. The exterior body 200 is provided with a latch section200 b. Therefore, the two pieces of the exterior body 200 can be coupledwithout fail.

The exterior body 200—into which the radio wave absorber 201 and thepolystyrene foam 202 are formed integrally—is considered to be formedinto a configuration where the polystyrene foam 202 is not interposedbetween the probe main body 40 and the radio wave absorber 201.

Here, the radiation field immunity system has been described thus far asthe embodiment of the present invention. However, the present inventioncan also be considered to be formed as a system which evaluates emission(EMI). This emission system is for evaluating whether or not theconductivity of a radiation field emitted from a device under test, suchas an electronic device, and intensity of radioactive interferenceexceed predetermined limit values.

The emission system is for measuring noise emitted from the device undertest. As in the case of immunity, measurement of noise is usuallyperformed within the radio wave shielded chamber 10 (see FIG. 1). Thestructure of the emission system employed for that case negates the needfor the antenna 20, the upstand 21, the cable 22, and an additionalradio wave absorber 11 (see FIG. 1) to be placed on the floor. Anunillustrated device under test is placed in a position where theantenna 20 is to be set. By means of such a configuration, the fieldintensity developing from a position spaced a given distance from thedevice under test is measured by the probe 30 (see FIG. 1).

EXAMPLES

Examples of the present invention will now be described.

In the examples, the probe 30 is set at an elevation equivalent to theelevation of the antenna 20. Tests were conducted while conditions, suchas attachment of the probe 30 and the shape of a radio wave absorber ofthe probe 30, were varied. The amplifier 52 was controlled whilefrequency sweep from 4000 MHz (4 GHz) to 6000 MHz (6 GHz) was beingperformed such that the field intensity measured by the probe 30 assumesa value of 10 V/m, whereby power of the amplifier 52 was measured.Specifically, the power required to maintain field intensity to 10 V/mwas measured. A radio wave absorber of so-called high carbon type formedby impregnating urethane with 3 to 5 mg/liter of carbon was used as aradio wave absorber. The concentration of carbon in the radio waveabsorber is constant.

FIGS. 15A and 15B are graphs showing test results, wherein the verticalaxis represents required power (W) and the horizontal axis represents afrequency (MHz). FIG. 16 is a graph showing variations computed from thetest results. As shown in FIGS. 15A, 15B and 16, tests were conducted insix modes while conditions were changed. FIG. 17 is a block diagramshowing the arrangement of the probe main body 40 of a third example.FIG. 18 is a block diagram showing a probe 30′ of a third comparativeexample.

First Example

In a first example, the radio wave absorber 160 of the embodiment (seeFIGS. 10A and 10B) was attached to the probe main body 40, to thusconstitute the probe 30. The test was conducted while the probe 30 wasfastened to the upstand 31. In this case, the pipe section 42 of theprobe main body 40 was fastened so as to become horizontal with respectto the antenna 20 (see FIG. 1). The upstand 31 (see FIG. 1) was formedfrom FRP (Fiber-Reinforced Plastics). A radio wave absorber, which wasformed from the same material as that of the radio wave absorber 160,was attached to the upstand 31. The diameter A (shown in FIG. 10A) ofthe head section 41 of the probe main body 40 is set to 10 cm, and asegment B (shown in FIG. 10A) by way of which the pipe section 42 wasexposed from the radio wave absorber 160 is set to 1 cm.

Under the conditions of the first example, the test results such asthose indicated by line (1) in FIG. 15A were obtained. As shown in FIG.16, the range of changes is 1.7 dB. As mentioned above, in the firstexample, fluctuations in the required power attributable to thefrequency are considerably small.

Second Example

In a second example, the radio wave absorber 160 (see FIGS. 10A and 10B)of the present example was attached to the probe main body 40, to thusform the probe 30. The test was carried out by attaching the probe 30 toan unillustrated polystyrene foam mount. In this case, the pipe section42 of the probe main body 40 was attached to the antenna 20 (see FIG. 1)so as to become horizontal to the same. Box-shaped polystyrene foam wasused in an inclined form as an unillustrated polystyrene foam mount.Specifically, the unillustrated polystyrene foam was inclined, therebyarranging the probe main body 40 so as to become horizontal to theantenna 20.

Under conditions of the second example, test results such as thoseindicated by line (2) in FIG. 15A were acquired. As shown in FIG. 16,the range of variations was 1.6 dB. As mentioned above, even in the caseof the second example, fluctuations in the required power attributableto a frequency were considerably small.

Third Example

In a third example, the radio wave absorber 160 (see FIGS. 10A and 10B)of the present example was attached to the probe main body 40, to thusconstitute the probe 30. The test was carried out by attaching the probe30 to the unillustrated polystyrene foam mount. In this case, as shownin FIG. 17, the probe main body 40 was inclined at a horizontal angle Cof 45 degrees with respect to the antenna 20 (see FIG. 1). Specifically,the probe main body 40 forms an inclination of 45 degrees with respectto the direction of a radio wave from the antenna 20.

Under the conditions of the third example, test results such as thoseindicated by line (3) shown in FIG. 15A were obtained. In this case, asshown in FIG. 16, the range of variations was 1.3 dB. Even in the caseof the third example, fluctuations in required power attributable to afrequency were considerably small.

First Comparative Example

A test was conducted, as a first comparative example, by attaching theprobe main body 40 to the unillustrated polystyrene foam mount at ahorizontal angle of 33.5 degrees and a vertical angle of 33.5 degreeswithout attachment of the radio wave absorber. A test result, such asthat indicated by line (4) in FIG. 15B, was obtained as a result of thefirst comparative example. As shown in FIG. 16, the range of variationswas 2.2 dB.

Second Comparative Example

A test was conducted, as a second comparative example, by attaching theprobe main body 40 to the antenna 20 of an FRP-made mast withoutattachment of the radio wave absorber. In the second comparativeexample, as indicated by line (5) in FIG. 15B, fluctuations in therequired power were great. As shown in FIG. 16, the range of changes was7.0 dB.

Third Comparative Example

As shown in FIG. 18, as a third comparative example, a cubic radio waveabsorber 210 was attached to the probe main body 40, to thus constitutea probe 30′. The probe 30′ was fastened to the mast made of FRP. In thecubic radio wave absorber 210, a large wall section 210 a was arrangedon the head section 41 of the probe main body 40. The radio waveabsorber 210 covered only the box section 43 of the pipe section 42 inthe probe main body 40. Most of the pipe section 42 was exposed.

Even in the third comparative example, fluctuations in the requiredpower were large, as indicated by line (6) in FIG. 15. As shown in FIG.16, the range of variations was 7.0 dB. Even in this case, the probe 30′shown in FIG. 18 is fastened so as to become horizontal to the antenna(see FIG. 1).

As mentioned above, in the first to third examples, the ranges ofvariations in the required power were smaller than those acquired in thefirst through third comparative examples, and frequency dependence wassmall. For instance, in the second and third comparative examples, themaximum required power and the minimum required power changed by afactor of five or thereabouts. Therefore, a piece of equipment meetingthe maximum required power, such as a power amplifier, is required, andlarger power consumption is required. For these reasons, difficulty isencountered in curtailing manufacturing cost and test cost. In contrast,in the case of the first through third examples, a difference betweenthe maximum required power and the minimum required power is small, andhence a piece of equipment, such as a power amplifier having a lowrating output, is sufficient. For these reasons, manufacturing cost andtest cost can be significantly curtailed.

It can be said that the larger the variations in transmission outputattributable to a frequency, the greater the influence of a wavereflected from a structure including the probe 30. Therefore, in thefirst through third examples involving small variations, the influenceof the variations can be diminished.

Moreover, according to the results of the first through thirdcomparative examples, variations in power can be said to becomeextremely large when the probe 30 is arranged horizontally. When themain body section of the probe 30 is covered with a radio wave absorberof the present embodiment, variations in power are reduced. Hence, thevariations are considered to be attributable to the influence of thewave reflected from the main body section.

As described with reference to the embodiment, occurrence of an error inmeasurement of an electromagnetic field probe may be prevented bysuppressing occurrence of a phenomenon of reflection of anelectromagnetic wave.

Although the present invention has been shown and described withreference to the embodiments, various changes and modifications will beapparent to those skilled in the art from the teachings herein. Suchchanges and modifications as are obvious are deemed to come within thespirit, scope and contemplation of the invention as defined in theappended claims.

1. An electromagnetic field probe comprising: an antenna section thatmeasures an electromagnetic field; a wire connected to the antennasection; a shielding member that shields the wire; a box section thatreceives an input of a measurement result of the antenna section by wayof the wire; and a radio wave absorber that surrounds circumferences ofthe shielding member and the box section, wherein the radio waveabsorber is provided with a portion having outer dimension and thicknessthat increase in accordance with a distance from the antenna section. 2.The electromagnetic field probe according to claim 1, wherein theshielding member is a pipe member in which the wire is providedtherethrough and supports the antenna section.
 3. The electromagneticfield probe according to claim 1, further comprising a retaining sectionthat retains the radio wave absorber by surrounding a circumference ofthe radio wave absorber.
 4. The electromagnetic field probe according toclaim 3, wherein the radio wave absorber is formed of urethane, and theretaining section is formed of polystyrene foam.
 5. The electromagneticfield probe according to claim 3, wherein the retaining sectionincludes: a first retaining section; and a second retaining section thatengages with the first retaining section, and wherein the firstretaining section and the second retaining section surround acircumference of the radio wave absorber.
 6. The electromagnetic fieldprobe according to claim 5, further comprising a boss provided on thefirst retaining section, wherein the second retaining section defines ahole section that engages with the boss of the first retaining section.7. A radiated immunity system for measuring an uniformity of anelectromagnetic field required for a radiated immunity test, theradiated immunity system comprising: a radiation antenna; an antennasection that measures an electromagnetic field by means of the radiationantenna; a wire connected to the antenna section; a shielding memberthat shields the wire; and a radio wave absorber that surrounds acircumference of the shielding member, the radio wave absorber havingouter dimension and thickness that increase in accordance with adistance from the antenna section.
 8. The radiated immunity systemaccording to claim 7, wherein the radio wave absorber includes: a firstradio wave absorbing section; and a second radio wave absorbing sectionthat is engaged with the first radio wave absorbing section, and whereinthe first radio wave absorbing section and the second radio waveabsorbing section cover the shielding member.
 9. The radiated immunitysystem according to claim 7, further comprising: a first retainingsection that surrounds a circumference of the radio wave absorber; and asecond retaining section that engages with the first retaining sectionand surrounds a circumference of the radio wave absorber.
 10. Theradiated immunity system according to claim 9, further comprising a bossprovided on the first retaining section, wherein the second retainingsection defines a hole section that engages with the boss of the firstretaining section.
 11. The radiated immunity system according to claim7, further comprising a structure body interposed between the shieldingmember and the radio wave absorber to receive a load of theelectromagnetic field probe.
 12. An electromagnetic field probe,comprising: an antenna section; a wire connected to the antenna section;a support member that supports the antenna section; and a longitudinalradio wave absorber surrounding a circumference of the support member,wherein the radio wave absorber has a proximal end section providedclose to the antenna section and a distal end section provided remotefrom the antenna section, wherein a cross-sectional area of the radiowave absorber increases in accordance with a distance from the proximalend section toward the distal end section, and wherein thecross-sectional area is configured to be maximum at an intermediateposition between the proximal end section and the distal end section orat the position of the distal end section.
 13. The electromagnetic fieldprobe according to claim 12 further comprising a box section that iscoupled to the support member and receives an input of a receivingresult performed by the antenna section by way of the wire, wherein theradio wave absorber covers a face of the box section facing the antennasection.
 14. The electromagnetic field probe according to claim 12,wherein the radio wave absorber includes a first radio wave absorbingsection, and a second radio wave absorbing section engaged with thefirst radio wave absorbing section, and wherein the first radio waveabsorbing section and the second radio wave absorbing section cover thesupport member.
 15. The electromagnetic field probe according to claim12, wherein the support member is a pipe member in which the wire isprovided therethrough and supports the antenna section.
 16. Theelectromagnetic field probe according to claim 12, wherein an outershape of the radio wave absorber is formed in a shape of ansubstantially truncated cone.
 17. The electromagnetic field probeaccording to claim 12, wherein an outer shape of the radio wave absorberis formed in a shape of an substantially truncated prismoid.
 18. Theelectromagnetic field probe according to claim 12, wherein the radiowave absorber has an outer shape formed by bulging a side surface of ansubstantially truncated cone.
 19. An electromagnetic field probecomprising: an antenna section that measures an electromagnetic field; awire connected to the antenna section; a shielding member that shieldsthe wire; a box section that receives an input of a measurement resultof the antenna section by way of the wire; and a radio wave absorberthat surrounds circumferences of the shielding member and the boxsection, wherein the radio wave absorber has a proximal end sectionprovided close to the antenna section and a distal end section providedremote from the antenna section, wherein a cross-sectional area of theradio wave absorber increases in accordance with a distance from theproximal end section toward the distal end section, and wherein thecross-sectional area is configured to be maximum at an intermediateposition between the proximal end section and the distal end section orat the position of the distal end section.
 20. The electromagnetic fieldprobe according to claim 19, wherein the shielding member is a pipemember in which the wire is provided therethrough and supports theantenna section.
 21. The electromagnetic field probe according to claim19, further comprising a retaining section that retains the radio waveabsorber by surrounding a circumference of the radio wave absorber. 22.The electromagnetic field probe according to claim 21, wherein the radiowave absorber is formed of urethane, and the retaining section is formedof polystyrene foam.
 23. The electromagnetic field probe according toclaim 21, wherein the retaining section includes: a first retainingsection; and a second retaining section that engages with the firstretaining section, and wherein he first and second retaining sectionssurround a circumference of the radio wave absorber.
 24. Theelectromagnetic field probe according to claim 23, further comprising aboss provided on the first retaining section, wherein the secondretaining section defines a hole section that engages with the boss ofthe first retaining section.
 25. A radiated immunity system formeasuring uniformity of an electromagnetic field required for a radiatedimmunity test, the radiated immunity system comprising: a radiationantenna; an antenna section that measures an electromagnetic field bymeans of the radiation antenna; a wire connected to the antenna section;a shielding member that shields the wire; and a radio wave absorber thatsurrounds a circumference of the shielding member, wherein the radiowave absorber has a proximal end section provided close to the antennasection of the electromagnetic field probe and a distal end sectionprovided remote from the antenna section, wherein a cross-sectional areaof the radio wave absorber increases in accordance with a distance fromthe proximal end section toward the distal end section; and wherein thecross-sectional area is configured to be maximum at an intermediateposition between the proximal end section and the distal end section orat the position of the distal end section.
 26. The radiated immunitysystem according to claim 25, wherein the radio wave absorber includes:a first radio wave absorbing section; and a second radio wave absorbingsection that is engaged with the first radio wave absorbing section, andwherein the first radio wave absorbing section and the second radio waveabsorbing section cover the shielding member.
 27. The radiated immunitysystem according to claim 25, further comprising: a first retainingsection that surrounds the radio wave absorber; and a second retainingsection that engages with the first retaining section and surrounds acircumference of the radio wave absorber.
 28. The radiated immunitysystem according to claim 27, further comprising a boss provided on thefirst retaining section, wherein the second retaining section defines ahole section that engages with the boss of the first retaining section.29. The radiated immunity system according to claim 25, furthercomprising a structure body interposed between the shielding member andthe radio wave absorber to receive a load of the electromagnetic fieldprobe.